The present invention relates to a method and an apparatus for detecting road circumstances around a traveling vehicle and a recording medium for storing a related software program. The present invention is applicable to a vehicle follow-up system or a distance warning system based on a radar system.
In a conventional vehicle follow-up control, a same lane judgement is performed to check whether the preceding vehicle is traveling on the same traffic lane as that of a traveling vehicle mounting a radar system (hereinafter referred to as system's vehicle).
For example, it is possible to use information obtainable from the steering sensor and the yaw rate sensor in judging whether the traffic lane is a straight lane or a curved lane. An estimated road shape or configuration will be obtained from this judgement. The same lane judgement is performed based on such an estimated road by checking whether the preceding vehicle and the system's vehicle exist on the same traffic lane of this estimated road.
However, the curvature of a traveling road changes flexibly or randomly. A straight road may suddenly change to a curved road or vice versa. In such a case, it is difficult to accurately obtain the estimated road. This leads to an error in the same lane judgement. In other words, the information obtainable from the steering sensor and the yaw rate sensor is limited to present conditions of the system's vehicle and therefore cannot predict the future behavior of the system's vehicle.
To solve such a problem, Unexamined Japanese Patent Publication No. 6-195600 discloses a laser radar system and proposes a method of estimating the road configuration based on the positional relationship between the traveling vehicle and reflectors provided along a road edge.
However, this conventional system has the following problems:
1 There are many roads along which no reflectors are provided. Thus, the usability of the above conventional system is limited to specific or high-grade roads. PA1 2 In general, many of highway roads are designed to have a clothoid curve whose curvature changes continuously or momentarily. Thus, an error will be caused if the same lane judgement is made based on only one curvature value. PA1 3 Furthermore, the laser-based radar technology cannot be simply applied to a radio wave type radar due to difference in their resolutions. In general, the radio wave type radar is inferior to the laser type radar in azimuth detecting capability. The level of reflected radar wave varies greatly depending on the angle between the emitted radar wave and a target object. Furthermore, the radio wave type radar is subjected to a multipath phenomenon caused by multiple reflections of radio wave.